Those are magic words to investors, both small and large, and Ginnie Maes -- securities guaranteed by the Government National Mortgage Association -- are considered among the safest investments you can make.

Ginnie Mae has guaranteed nearly $240 billion in securities since 1968 without a blemish, according to Jack Flynn, spokesman for the Washington public affairs office of the federal Department of Housing and Urban Development.

A part of HUD, Ginnie Mae regenerates capital for mortgages by issuing securities backed by pools of Federal Housing Administration-insured, Veterans Administration-guaranteed or Farmers Home Administration-backed home mortgages.

The government guarantees the timely payment of principal and interest.

However, in recent years, the performance of companies such as Government Securities Inc. in Tampa -- a government securities dealer that filed bankruptcy late last year and left the fate of hundreds of investors' money up in the air -- has prompted some people to question the viability of Ginnie Mae investments.

The Florida Division of Securities has accused the company of defrauding its investors.

Like a number of financial advisers, Joe Bert, of Certified Financial Services in Altamonte Springs, recommends dealing with a brokerage affiliated with the National Association of Securities Dealers and registered with the Securities and Exchange Commission.

Brokerages dealing only in government securities essentially are unregulated by the federal government or the state of Florida.

Chris Anderson, director of securities for the state Division of Securities, said there are dealers in Florida operating solely in government securities ''who do what they're supposed to do.''

But, with others, an investor can get stung, he noted.

The key to safety is to check carefully before investing, Anderson said.

''There are some trite but truisms in effect here,'' he added. ''Never invest more than you can afford to lose. Another is if it sounds too good to be true, it probably isn't.''

There's more than one way to invest in Ginnie Maes.

You can go to a major brokerage house or bank and buy a certificate, which can be registered in your name and you can have it delivered so you have it in hand.

The certificates are sold in minimum amounts of $25,000.

However, small investors can invest in Ginnie Maes both through mutual funds or individual unit trusts in amounts as low as $1,000.

The trusts essentially purchase certificates and distribute payments.

The mutual funds are constantly buying and selling securities in an effort to boost their overall yield.

Small investors are, in effect, buying a participation in a Ginnie Mae pool.

Ray Parkins, president of The Parkins Investment Cos., hasn't recommended investing in government securities such as Ginnie Maes in recent years because of the effect of interest rate swings on their market value. ''There are better opportunities than government securities,'' he said. A Ginnie Mae reacts to interest rate changes much like a bond. If an investor is holding an 11 percent Ginnie Mae and interest rates drop, say to 8 percent, the market value of the Ginnie Mae would climb substantially. If interest rates soared, say to 17 percent, the value of the 11 percent Ginnie Mae would fall considerably.

If he were to invest in Ginnie Maes, Parkins said he would would use the mutual fund approach because the yield might be increased through the astute purchase of new certificates.

Repple also noted that the mortgages backing the security often are paid off before their maturity, and that can be disruputive to an investor's plans. Herb Sunshine, of A.G. Edwards & Sons, Orlando, said Ginnie Mae investors sometimes don't realize the check they receive contains both a return of a portion of the principal as well as interest.

Such an investor can deplete his capital without realizing it, he noted.

For safety in any investment, Sunshine suggested dealing with registered brokerages. He also said investors shouldn't be afraid to ask questions and for the names of clients.

''Call up the (Florida) Division of Securities and ask if they've had any complaints,'' he said. ''If you have any doubts, don't spend your money.''

Full-service brokerage houses must be registered with the SEC. That registration mandates that the brokerage participate in the Security Investors Protection Corp., a private non-profit agency created by Congress in 1970 to bolster investor protections.

Supported by assessments on brokerage houses, the corporation also has a backup line of credit of $1 billion with the U.S. Treasury, said Stephen Harbeck, associate general counsel for the corporation.

If a brokerage is in trouble, the corporation can do a number of things to protect the investor, including appointing a trustee to take control and transferring accounts to viable brokerages. An investor can be protected up to $500,000, including up to $100,000 in cash placed with a broker to purchase securities.

Harbeck said the corporation was created to provide a means to deal with stock brokers unable to meet their obligations, not as an account insurance program.

As the state alleges in the Government Securities case in Tampa, sometimes investors can lose through fraud. The state contends the company didn't use all the investors' money to buy securities.